Fluid ejection with micropumps and pressure-difference based fluid flow

ABSTRACT

The fluid ejection device includes a plurality of nozzles and a plurality of ejection chambers that includes a respective ejection chamber fluidically coupled to a respective nozzle. A plurality of inlet passages are fluidically coupled to the ejection chambers and input fluid to the ejection chambers at a first pressure. A plurality of outlet passages are fluidically coupled to the ejection chambers and output fluid from the ejection chambers at a second pressure that is less than the first pressure. Fluid circulates through the ejection chambers based on the pressure difference between the first and second pressure. The fluid ejection device also includes at least one micropump fluidically coupled to at least one ejection chamber to pump fluid through the at least one ejection chamber.

BACKGROUND

A fluid ejection device is a component of a fluid ejection system thatejects fluid. A fluid ejection device includes a number of fluidejecting nozzles. Through these nozzles, fluid, such as ink and fusingagent among others, is ejected. An ejection chamber holds an amount offluid to be ejected and a fluid actuator within the ejection chamberoperates to eject the fluid through the nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various examples of the principlesdescribed herein and are part of the specification. The illustratedexamples are given merely for illustration, and do not limit the scopeof the claims.

FIGS. 1A and 1B are diagrams of a fluid ejection device with micropumpsand pressure-difference based fluid flow, according to an example of theprinciples described herein.

FIG. 2 is a cross-sectional diagram of a fluid ejection device withmicropumps and pressure-difference based fluid flow with an upstreammicropump, according to an example of the principles described herein.

FIG. 3 is a cross-sectional diagram of a fluid ejection device withmicropumps and pressure-difference based fluid flow with a downstreampump, according to an example of the principles described herein.

FIGS. 4A and 4B are cross-sectional diagram of a fluid ejection devicewith micropumps and pressure-difference based fluid circulation with apiezoelectric membrane pump, according to an example of the principlesdescribed herein.

FIGS. 5A and 5B are cross-sectional diagram of a fluid ejection devicewith micropumps and pressure-difference based fluid circulation with apiezoelectric membrane pump, according to another example of theprinciples described herein.

FIG. 6 is a flowchart of a method for fluid ejection with micropumps andpressure-difference based fluid flow, according to an example of theprinciples described herein.

FIG. 7 is an isometric view of a fluid ejection device with micropumpsand pressure-difference based fluid flow, according to another exampleof the principles described herein.

FIG. 8 is a planar view of the fluid ejection device with micropumps andpressure-difference based fluid flow, according to an example of theprinciples described herein.

FIGS. 9A and 9B are cross-sectionals view of the fluid ejection devicewith micropumps and pressure-difference based fluid flow, according toan example of the principles described herein.

FIG. 10 is a flowchart of a method for fluid ejection with micropumpsand pressure-difference based fluid flow, according to another exampleof the principles described herein.

FIG. 11 is a planar view of a fluid ejection device with micropumps andpressure-difference based fluid flow, according to another example ofthe principles described herein.

FIG. 12 is a diagram of a fluid ejection device with micropumps andpressure-difference based fluid flow, according to another example ofthe principles described herein.

FIG. 13 is a diagram of a fluid ejection device with micropumps andpressure-difference based fluid flow, according to another example ofthe principles described herein.

FIG. 14 is a diagram of a fluid ejection device with micropumps andpressure-difference based fluid flow, according to another example ofthe principles described herein.

FIGS. 15A-15C are views of a fluid ejection devices with micropumps andpressure-difference based fluid flow, according to another example ofthe principles described herein.

FIG. 16 is a block diagram of a fluid ejection device with micropumpsand pressure-difference based fluid flow, according to another exampleof the principles described herein.

FIG. 17 is a block diagram of a fluid ejection system with micropumpsand pressure-difference based fluid flow, according to another exampleof the principles described herein.

DETAILED DESCRIPTION

Fluid ejection devices, as used herein, may describe a variety of typesof integrated devices with which small volumes of fluid may be ejected.In a specific example, these fluid ejection devices are found in anynumber of printing devices such as inkjet printers, multi-functionprinters (MFPs), and additive manufacturing apparatuses. The fluidicsystems in these devices are used for precisely, and rapidly, dispensingsmall quantities of fluid. For example, in an additive manufacturingapparatus, the fluid ejection system dispenses fusing agent. The fusingagent is deposited on a build material, which fusing agent facilitatesthe hardening of build material to form a three-dimensional product.

Other fluid ejection systems dispense ink on a two-dimensional printmedium such as paper. For example, during inkjet printing, fluid isdirected to a fluid ejection device. Depending on the content to beprinted, the system in which the fluid ejection devices is disposeddetermines the time and position at which the ink drops are to bereleased/ejected onto the print medium. In this way, the fluid ejectiondevice releases multiple ink drops over a predefined area to produce arepresentation of the image content to be printed. Besides paper, otherforms of print media may also be used. Accordingly, as has beendescribed, the devices and methods described herein may be implementedin two-dimensional printing, i.e., depositing fluid on a substrate, andin three-dimensional printing, i.e., depositing a fusing agent or otherfunctional agent on a material base to form a three-dimensional printedproduct.

As will be appreciated, examples provided herein may be formed byperforming various microfabrication and/or micromachining processes onat least one substrate to form and/or connect structures and/orcomponents. The substrate may comprise a silicon based wafer or othersuch similar materials used for microfabricated devices (e.g., glass,gallium arsenide, metals, ceramics, plastics, etc.). Examples maycomprise microfluidic channels, fluid actuators, nozzles, volumetricchambers, or any combination thereof. Microfluidic channels and/orchambers may be formed by performing etching, microfabrication (e.g.,photolithography), micromachining processes, or any combination thereofin a substrate. Accordingly, microfluidic channels and/or chambers maybe defined by surfaces fabricated in the substrate of a microfluidicdevice. As used herein, a microfluidic channel or a microfluidic chambermay be so described because such channels and chambers may facilitatestorage and conveyance of volumes of fluid in the nanoliter scale,picoliter scale, microliter scale, etc.

Examples provided herein may implement fluid actuators, where such fluidactuators may comprise thermal actuators, piezo-membrane actuators,electrostatic actuators, mechanical/impact driven membrane actuators,magnetostrictive drive actuators, electrochemical actuators, other suchmicrodevices, or any combination thereof. In some examples, a fluidactuator may be disposed in a microfluidic volume, such as a channel orchamber. Actuation of the fluid actuator may cause displacement of fluidproximate the fluid actuator, and such fluid displacement, in turn, mayresult in flow of fluid in the microfluidic volume. Accordingly, suchexample fluid actuators disposed in microfluidic volumes to cause fluidflow therein may be referred to as “micropumps.” In some examples, afluid actuator may be disposed in a microfluidic chamber fluidicallycoupled to a nozzle through which fluid drops may be ejected. In theseexamples, actuation of the fluid actuator may cause displacement offluid proximate the fluid actuator such that a fluid drop may be ejectedvia the nozzle. Accordingly, such example fluid actuators disposed inejection chambers fluidically coupled to nozzles may be referred to as“fluid ejectors.”

While such fluidic ejection devices have increased in efficiency inejecting various types of fluid, enhancements to their operation canyield increased performance. As one example, the operation of someejectors may alter the composition of the fluid passing through theejection chamber. For example, a thermal ejector heats up in response toan applied voltage. As the thermal ejector heats up, a portion of thefluid in an ejection chamber vaporizes to form a bubble. This bubblepushes fluid out the nozzle and onto the print medium. When the ejectoris not firing, portions of the fluid evaporate through the nozzle suchthat the fluid becomes depleted of water or other volatile solvents. Inother words, the fluid becomes more concentrated and more viscous. Fluidthat is depleted of water can negatively influence the nozzles and canresult in reduced fluid quality.

This is partly addressed by circulating the fluid passing to the nozzleand/or to the chamber. However, the desirable impact of recirculatingmechanisms is reduced due to fluid mechanics. For example, fluid issupplied to the fluid ejection device die via a fluid supply system. Afluid supply system may include fluid supply components, such as pumps,regulators, tanks, and other such components that apply fluid pressuredifferentials to the fluid supply system and fluid ejection devicesconnected thereto to thereby drive fluid through these fluid supplycomponents and fluid ejection devices connected thereto. In some fluidejection systems, fluidic aspects of fluid ejection devices implementedtherein may limit the effects of this fluid flow in the chambers and thefluid passages of the fluid ejection devices.

Accordingly, the present specification describes a fluid ejection devicethat solves these and other issues. Specifically, the presentspecification describes a fluid ejection device and method that forceflow through an ejection chamber via a pressure differential. The fluidejection devices may also adjust fluid flow through ejection chamberswith at least one micropump located proximate to and fluidicallyconnected with the ejection chambers. In these examples, the fluidejection device includes inlet passages and outlet passages that arefluidically coupled to channels on the back of the fluid ejection devicehaving different fluid pressures.

Such a flow generated by a pressure differential cools the fluidejection device which may be heated by actuating thermal ejectors andensures uniformly printed fluid, and provides fresh fluid to the nozzle.However, pressure differentials by themselves may vary across differentnozzles due to pressure drops caused by different path lengths,geometries, etc. Moreover, if the pressure differential is too great,excessive flow rates may result, which can lead to changes incomposition of the fluid, i.e. solvent depletion. Still further, byalways providing fresh fluid to the nozzle, the evaporation rate ofsolvents can increase, which as noted above can cause a change in thecomposition of the fluid, resulting in a decreased print quality.Moreover, such pressure differential flow is applied across multiplenozzles. Such a bulk operation therefore operates on all nozzles thesame, regardless of differences between the nozzles.

Accordingly, examples provided herein further include at least onemicropump to facilitate device-level and/or chamber-level control offluid flow through to thereby increase the operating efficiency of afluid ejection system. Specifically, a micropump allows forprogrammatically applying an actuation pulse to individual micropumps.Local heating can also be somewhat mitigated by actuating micropumpsjust before ejecting drops with a given fluid ejector.

Accordingly, the present specification describes a hybrid system forfacilitating fluid flow through an ejection chamber, which fluid flowenables through-chamber circulation of fluid driven at least in part bysystem-level pressure differentials and at least in part by micropumpactuation. In some examples, such through-chamber circulation of fluidmay be referred to as micro-recirculation. In particular, for a fluidejection device, such as a printhead or printhead module, fluid iscirculated through each ejection chamber of the fluid ejection device atleast in part by supplying and collecting the fluid at pressuredifferentials. For example, fluid supplied to manifolds, channels, andultimately ejection chambers may be driven at a first pressure, andcollection of fluid from the chambers, channels, and manifolds may bedriven at a second pressure that is less than the first pressure. In onespecific example, the fluid supply may be driven at a positive pressure,and the fluid collection may be driven by a vacuum. In another example,the fluid pressure of the fluid collection may be less such that fluidfrom the supply is driven into the fluid collection path.

Furthermore, the fluid flow through the ejection chamber may beselectively adjusted by actuation of a micropump that is proximate to,and fluidically connected to, the ejection chamber. For example, whilepressure differentials may generate a flow through an ejection chamberat a particular rate, F1, the flow rate may be temporarily adjusted to adifferent value, F2, via actuation of the micropump. In some examples,actuation of the micropump may increase the flow rate. That is,actuation of the micropump may increase the pressure differentialbetween the inlet and the outlet of the ejection chamber. In otherexamples, actuation of the micropump may decrease the flow rate. Thatis, actuation of the micropump may reduce the pressure differentialbetween the inlet and the outlet of the ejection chamber. Thus acustomized flow may be generated through an ejection chamber based onthe selective activation, and placement, of such micropumps throughoutthe fluid ejection device. Such a customized flow rate facilitatescustomization of the operation of the fluid ejection device based onsystem and fluid characteristics

Accordingly, differential pressures can be augmented or reduced bymicropumps to tailor the flow to ejection chambers and/or nozzles asdesired to compensate for pressure non-uniformities caused by geometryeffects. The placement of the ejector relative to the nozzle can bechosen to augment flow in low flow regions (by placing the pump upstreamof the ejector) and/or decrease the flow in high flow regions (byplacing the pump downstream of the ejector). The temperature increasedue to pump firing can be mitigated by the cooling effect of thedifferential pressure method. In such examples, positioning of amicropump relative to the ejection chamber may correspond to whetheractuation of the micropump increases or decreases a flow rate of fluidthrough the chamber. For example, in a thermal actuator-based micropump,if the micropump is positioned on the inlet passage side of the ejectionchamber, actuation of the micropump may increase a flow rate of fluidthrough the ejection chamber. Conversely, if the micropump is positionedon the outlet passage side of the ejection chamber, actuation of themicropump may decrease a flow rate of fluid through the ejectionchamber. In another example, in a membrane-based actuator micropump,deflection of the membrane into the microvolume or away from themicrovolume may cause different flow characteristics.

Specifically, the present specification describes a fluid ejectiondevice. The fluid ejection device includes a plurality of nozzles and aplurality of ejection chambers. The plurality of ejection chambersincludes a respective ejection chamber which is fluidically coupled to arespective nozzle of the plurality of nozzles. The fluid ejection devicealso includes a plurality of inlet passages. The inlet passages arefluidically coupled to the ejection chambers and input fluid to theejection chambers at a first pressure. The fluid ejection device alsoincludes a plurality of outlet passages. The plurality of outletpassages are fluidically coupled to the ejection chambers and outputsfluid from the ejection chamber at a second pressure that is less thanthe first pressure. Accordingly fluid circulates through the ejectionchambers based on the pressure difference between the first pressure andthe second pressure. The fluid ejection device also includes at leastone micropump fluidically coupled to at least one ejection chamber topump fluid through the at least one ejection chamber.

In another example, the fluid ejection device includes a plurality ofnozzles and a plurality of ejection chambers. The plurality of ejectionchambers includes a respective ejection chamber which is fluidicallycoupled to a respective nozzle of the plurality of nozzles. The fluidejection device also includes a plurality of inlet passages whichincludes a respective inlet passage fluidically coupled to therespective ejection chamber. The fluid ejection device also includes aplurality of outlet passages which includes a respective outlet passagefluidically coupled to the respective ejection chamber. In this example,the fluid ejection device includes at least one input channel. The atleast one input channel 1) is fluidically coupled to at least a subsetof inlet passages of the plurality of inlet passages and 2) suppliesfluid to the subset of inlet passages at a first pressure. The fluidejection device also includes at least one output channel. The at leastone output channel 1) is fluidically coupled to at least a subset ofoutlet passages of the plurality of outlet passages and 2) receivesfluid from the subset of outlet passages at a second pressure differentthan the first pressure to facilitate fluid circulation throughrespective ejection chambers fluidically coupled to the subset of inletpassages and the subset of outlet passages. The fluid ejection devicealso includes at least one micropump fluidically coupled to at least oneejection chamber to pump fluid through the at least one ejectionchamber.

The present specification also describes a method. According to themethod, fluid is circulated through a plurality of ejection chambers ata first flow rate by 1) supplying fluid to the plurality of ejectionchambers at a first pressure and 2) collecting fluid from the pluralityof ejection chambers at a second pressure that is lower than the firstpressure. The circulation of fluid is selectively adjusted through theplurality of ejection chambers to a second flow rate by actuating atleast one micropump fluidically coupled to the plurality of ejectionchambers.

Turning now to the figures, FIGS. 1A and 1B are diagrams of a fluidejection device (100) with micropumps (108) and pressure-differencebased fluid flow, according to an example of the principles describedherein. Specifically, FIG. 1A is an isometric view and FIG. 1B is across-sectional view taken along the line A-A from FIG. 1A. As describedabove, the fluid ejection device (100) refers to a component of a fluidejection system used in depositing fluids onto a substrate. To carry outsuch fluid ejection, the fluid ejection device (100) includes a varietyof components. For example, the fluid ejection device (100) includes aplurality of nozzles (102). Fluid is expelled by the fluid ejectiondevice (100) through the nozzles (102). For simplicity in FIG. 1A, onenozzle (102) has been indicated with a reference number. Moreover, itshould be noted that the relative size of the nozzles (102) and thefluid ejection device (100) are not to scale, with the nozzles (102)being enlarged for purposes of illustration.

The nozzles (102) of the fluid ejection device (100) may be arranged incolumns or arrays such that properly sequenced ejection of fluid fromthe nozzles (102) causes characters, symbols, and/or other graphics orimages to be printed on the print medium as the fluid ejection device(100) and print medium are moved relative to each other.

The fluid ejection device (100) may be coupled to a controller thatcontrols the fluid ejection device (100) in ejecting fluid from thenozzles (102). For example, the controller defines a pattern of ejectedfluid drops that form characters, symbols, and/or other graphics orimages on the print medium. The pattern of ejected fluid drops isdetermined by the print job commands and/or command parameters receivedfrom a computing device.

The fluid ejection device (100) may be formed of various layers. Forexample, a nozzle substrate (104) may define the ejection chambers andnozzles (102). The nozzle substrate (104) may be formed of SU-8 or othermaterial. Other layers of the fluid ejection device (100) may be formedof other layers.

Turning now to FIG. 1B, the fluid ejection device (100) also includes aplurality of ejection chambers (106). The ejection chambers (106) holdan amount of fluid to be ejected through the nozzle (102). Accordingly,a respective ejection chamber (106) of the plurality is fluidicallycoupled to a respective nozzle (102) of the plurality. As describedabove, the ejection chamber (106) and nozzle (102) may be defined in anozzle substrate (104) formed of a material such as SU-8.

During fluid ejection, fluid is depleted from the ejection chamber(106). Accordingly, the fluid ejection device (100) includes a pluralityof inlet passages (110) and a plurality of outlet passage (112). Aninlet passage (110) is fluidically coupled to an ejection chamber (106)and supplies fluid to the ejection chamber (106). An outlet passage(112) is also fluidically coupled to the ejection chamber (106) andcollects fluid from the ejection chamber (106). In some examples, theinlet fluid pressure is different than the outlet fluid pressure. Forexample, the inlet passage (110) may supply fluid to the ejectionchamber (106) at a first pressure, P1 and the outlet passage (112) maycollect fluid from the ejection chamber (106) at a second pressure, P2.The second pressure, P2, may be less than the first pressure, P1, suchthat a pressure differential exists. Such pressures may be generated byrespective regulators coupled to the inlet passage (110) and the outletpassage (112).

This pressure differential generates a flow (114) through the ejectionchamber (106). Such a flow (114) facilitates the replenishment of fluidthrough the ejection chamber (106) and also facilitates the expulsion ofunused fluid from the ejection chamber (106). Thus, a recirculation loopis generated.

In some examples, the passages (110, 112) and ejection chamber (106) maybe micro-fluidic structures. In this example, the micro-fluidic passages(110, 112) and micro-fluidic ejection chamber (106) form amicro-recirculation loop. A micro-fluidic structure may be ofsufficiently small size (e.g., of nanometer sized scale, micrometersized scale, millimeter sized scale, etc.) to facilitate conveyance ofsmall volumes of fluid (e.g., picoliter scale, nanoliter scale,microliter scale, milliliter scale, etc.). Such micro-structures preventsedimentation of the fluid passing there through and ensures that freshfluid is available within the ejection chamber (106).

In some cases, it may be desirable to adjust the rate of flow throughthe ejection chamber (106). Accordingly, the fluid ejection device (100)includes at least one micropump (108). A micropump (108) is fluidicallycoupled to the ejection chamber (106) to pump fluid through the ejectionchamber (106). In some examples, as depicted in FIG. 1B, the micropump(108) may be disposed within the ejection chamber (106), but in otherexamples as depicted below, the micropump (108) may be disposed atdifferent locations within the fluid ejection device (100). As will bedescribed in the following figures, the micropump (108) may include afiring resistor or other thermal device, a piezoelectric element, orother mechanism for ejecting fluid from the ejection chamber (106).

Accordingly, such a fluid ejection device provides pressure-differencebased flow which may cool the fluid ejection device (100) components andcan ensure print uniformity. Moreover, by including a micropump (108),individual flow rates can be generated at each nozzle (102). Moreover,the addition of the micropump (108) provides another tool to increase ordecrease the flow rate through an ejection chamber (106). Thus,increased control of flow rates is provided, which flow rates can becontrolled per-nozzle (102), thus enhancing the overall control of theprinting operation and quality.

FIG. 2 is a cross-sectional diagram of a fluid ejection device (100)with micropumps (108) and pressure-difference based fluid flow with anupstream micropump (108), according to an example of the principlesdescribed herein. As described above, the fluid micropump (108) may beof varying types. For example, the fluid micropump (108) may be athermal resistor. The thermal resistor heats up in response to anapplied voltage. As the thermal resistor heats up, a portion of thefluid in the ejection chamber (106) vaporizes to form a bubble (216).This bubble (216) pushes fluid towards the inlet passage (110) and theoutlet passage (112). The pressure wave generated by the drive bubble(216) dissipates at the inlet passage (110) and the outlet passage (112)due to the large volume of fluid. As the vaporized fluid bubble (216)collapses, fluid is drawn back via capillary forces. The ejectionchamber (106) refills with fluid more readily from the nearest plenumcreating a net flow. For example in FIG. 2, the net flow will be from P1towards P2, due to the proximity of the micropump (108) to the inletpassage (110). Thus, the pressure drive recirculation is reinforced.

That is, the location of the micropump (108) may affect whether a flowrate through the ejection chamber (106) increases or decrease. Forexample, as described above, in cases where the fluid micropump (108) isupstream of a nozzle (102), flow rate increases through the ejectionchamber (106). It may be desirable to place the micropump (108) upstreamin regions of low flow as compared to other regions on the fluidicejection device (100). In some examples, different nozzles (102) withina fluid ejection device (100) may have corresponding micropumps (108)disposed at different locations. Accordingly, fluid flow throughindividual nozzles (102) may be tailored based on different existingcharacteristics or different desired operating characteristics for eachnozzle (102).

Returning to the flow, in this example, the flow (218) resulting fromthe formation of the vapor bubble (216), augments the pressuredifferential driven flow (114) resulting from a pressure differencebetween P1 and P2 to result in a flow through the ejection chamber (106)that is greater than the flow rate based solely on the pressuredifferential. In this example, the micropump (108) may be referred to asa boost pump.

FIG. 3 is a cross-sectional diagram of a fluid ejection device (100)with micropumps (108) and pressure-difference based fluid flow with adownstream micropump (108), according to an example of the principlesdescribed herein. As described above, the location of the micropump(108) may affect whether a flow rate through the ejection chamber (106)increases or decreases. In the example, depicted in FIG. 3, themicropump (108) is downstream of a nozzle (102) and decreases a flowrate through the ejection chamber (106). It may be desirable to placethe fluid micropump (108) downstream in regions of high flow as comparedto other regions on the fluidic ejection device (100).

In this example, the flow (320) resulting from the formation of thevapor bubble (216), counters the pressure differential driven flow (114)resulting from a pressure difference between P1 and P2 to result in aflow through the ejection chamber (106) that is less than the flow ratebased solely on the pressure differential.

FIGS. 4A and 4B are cross-sectional diagrams of a fluid ejection device(100) with micropumps (108) and pressure-difference based fluid flowwith a piezoelectric membrane pump (108), according to an example of theprinciples described herein. That is, in these examples, the micropump(108) includes a piezoelectric membrane (422). As a voltage is applied,the piezoelectric membrane (422) deflects which generates a pressurepulse in the ejection chamber (106) that causes displacement of fluidwhich results in a net flow of fluid.

The direction of the net fluid flow resulting from the deflection isbased on an initial and secondary state of the piezoelectric membrane(422). For example, as depicted in FIG. 4A, the piezoelectric membrane(422) may have an initially concave position. In this example, a flow(114) resulting from the pressure differential may exist through theejection chamber (106). An applied voltage causes the piezoelectricmembrane (422) to deflect to a flat position as indicated in FIG. 4B. Aflow (424) resulting from the deflection of the piezoelectric membrane(422), augments the pressure differential driven flow (114) to result ina flow through the ejection chamber (106) that is greater than the flowrate based solely on the pressure differential.

FIGS. 5A and 5B are cross-sectional diagrams of a fluid ejection device(100) with micropumps (108) and pressure-difference based fluid flowwith a piezoelectric membrane pump (108), according to an example of theprinciples described herein. In the example depicted in FIGS. 5A and 5B,the piezoelectric membrane (422) may have an initially flat position asdepicted in FIG. 5A. In this example, a flow (114) resulting from thepressure differential may exist through the ejection chamber (106). Anapplied voltage causes the piezoelectric membrane (422) to deflect to aconcave position as indicated in FIG. 5B. A flow (526) resulting fromthe deflection of the piezoelectric membrane (422) to the concaveposition, counters the pressure differential driven flow (114) to resultin a flow through the ejection chamber (106) that is less than the flowrate based solely on the pressure differential. Note that while FIGS.4A, 4B, 5A, and 5B depict particular initial and deflected positions,other initial and deflected positions may be implemented in accordancewith the principles described herein.

FIG. 6 is a flowchart of a method (600) for fluid ejection withmicropumps (FIG. 1, 108) and pressure-difference based fluid flow,according to an example of the principles described herein. The method(600) as described herein, maintains a pressure differential or gradientacross the ejection chambers (FIG. 1B, 106) to circulate fluid acrossthe ejection chambers (FIG. 1B, 106). According to the method (500)fluid, such as ink or additive manufacturing agents, is circulated(block 601) through a plurality of ejection chambers (FIG. 1B, 106).Specifically, the fluid is circulated (block 601) at a first flow rate.The first flow rate may be defined by a pressure differential betweeninlet passages (FIG. 1B, 110) and outlet passages (FIG. 1B, 112)fluidically coupled to the ejection chamber (FIG. 1B, 106). That is, aninlet passage (FIG. 1B, 110) may be coupled to an input regulator whichestablishes a first pressure for the incoming fluid. Accordingly, afluid is supplied to the plurality of ejection chambers (FIG. 1B, 106)at a first pressure. An outlet passage (FIG. 1B, 112) may be coupled toan output regulator which establishes a second fluid pressure for theoutgoing fluid. Accordingly, a fluid is collected from the plurality ofejection chambers (FIG. 1B, 106) at a second pressure. The secondpressure may be less than the first pressure such that a pressuredifferential exists, which pressure differential drives fluid from theinlet passage (FIG. 1B, 110) to the outlet passage (FIG. 1B, 112).

In some examples, circulating (block 601) the fluid as described hereinmay include inputting fluid at the first pressure to input channels thatare fluidically coupled to respective ejection chambers (FIG. 1B, 106)and to output the fluid at a second pressure from output channels thatare fluidically coupled to respective ejection chambers (FIG. 1B, 106).This may be performed by a pressurized fluid source. Specifically, fluidunder pressure is supplied to an inlet passage (FIG. 1B, 110) from apressurized fluid source that is remote from the fluid ejection device(100). A pressure differential is maintained across the ejectionchambers (106) with the fluid supplied by the pressurized fluid source.The pressure differential causes fluid to circulate across the ejectionchamber (FIG. 1B, 106) to inhibit particle settling and to transfer heataway from the ejection chamber (FIG. 1B, 106). In one implementation,the pressure differential created across the ejection chamber (FIG. 1B,106) is at least 0.1 inch we (inches water column).

As described above, for any number of reasons it may be desirable tochange the flow rate. For example, an increased flow rate may increasethe quality of fluid passed to the nozzle (FIG. 1A, 102) and a decreasedflow rate may reduce the effects of excess flow rates, i.e.,evaporation, decap, etc. Moreover, changing the flow rate may be done inorder to align the flow rates of various nozzles (FIG. 1A, 102) on afluid ejection device (FIG. 1A, 100).

As such, the method (600) includes selectively adjusting (block 602)circulation within at least one ejection chamber (FIG. 1B, 106). Thiscan be done by actuating at least one micropump (FIG. 1B, 108)fluidically coupled to the plurality of ejection chambers (FIG. 1B,106). As described above, the positioning as well as initial conditionsof the micropump (FIG. 1B, 108) may define how actuation of thatmicropump (FIG. 1B, 108) alters the net fluid flow through the ejectionchambers (FIG. 1B, 106). Accordingly, a wide variety of adjustments arepossible based on different circumstances within the fluid ejectiondevice (FIG. 1, 100).

FIG. 7 is an isometric view of a fluid ejection device (100) withmicropumps (108) and pressure-difference based fluid flow, according toanother example of the principles described herein. Note that in FIG. 7,the layer that includes the nozzles (FIG. 1A, 102) has been removed toexpose the underlying components.

In some examples, fluid is passed to the plurality of inlet passages(110) via at least one input channel (728). The at least one inputchannel (728) is indicated in dashed lines in FIG. 7 indicating itsplace beneath the layer that forms the inlet passages (110), outletpassages (112) and in which the micropump (108) and ejector (734) areformed. Note that for simplicity, in FIG. 7 a single instance ofdifferent components is indicated with a reference number.

Returning to the at least one input channel (728), the at least oneinput channel (728) is fluidically coupled to at least a subset of inletpassages (110) of the plurality.

In some examples, fluid is passed from the plurality of outlet passages(112) via at least one output channel (730). The at least one fluidoutput channel (730) is indicated in dashed lines in FIG. 7 indicatingits place beneath the layer that forms the inlet passages (110), outletpassages (112) and in which the micropump (108) and ejector (734) areformed. That is, the fluid ejection device (100) includes a channelsubstrate in which the input channel (728) and output channel (730) areformed. The channel substrate may be formed of silicon.

Returning to the at least one output channel (730), the at least oneoutput channel (730) is fluidically coupled to at least a subset ofoutlet passages (112) of the plurality. The input channel (728) andoutput channel (730) are separated from one another by a rib (736)arranged under the ejector (734) and between the inlet passages (110)and the outlet passages (112). Such a rib (736) provides structuralrigidity against mechanical and gravitational force existent within thesystem.

FIG. 7 also depicts an example wherein adjacent ejection chambers (FIG.1B, 106) are separated by chamber walls (732) to more particularlyseparate the ejection chambers (FIG. 1B, 106) and generate a morespecific and efficient fluid flow.

In this example, fluid flows through the input channel (728) and passesthrough the various inlet passages (110), it then flows perpendicularacross the ejector (734) where it is ejected. Fluid that is not ejectedis directed, via differential pressures between the inlet passages (110)and the outlet passages (112) to the output channel (730). That is, asdepicted in FIG. 7, the flow between the passages (110, 112) isperpendicular to the flow through the channels (728, 730). While FIG. 7depicts the micropump (108) between an inlet passage (110) and theejector (734), in other examples as depicted above, the micropump (108)may be disposed between the ejector (734) and an outlet passage (112).

FIG. 8 is a planar view of the fluid ejection device (100) withmicropumps (108) and pressure-difference based fluid flow, according toan example of the principles described herein. FIG. 8 clearly shows thefluid path through the fluid ejection device (100). Note that in FIG. 8,a single instance of multiple components are indicated with referencenumbers.

Returning to the fluid flow, fluid passes into an input channel (728)which may be disposed under an inlet passage (110). The fluid thenpasses through the inlet passage (110) where it is directed through theejection chamber (FIG. 1B, 106) past the ejector (734). The ejector(734) is a component of the fluid ejection device (100) that operates toexpel fluid through a nozzle (102). As with the micropump (108), theejector (734) may be a thermal resistor, a piezoelectric component, orsome other mechanical device. When activated, the ejector (734) createsenergy which expels fluid through the nozzle (102).

Fluid that is not expelled is passed to the outlet passage (112) whereit is transferred to the output channel (730). Thus, the fluid ejectiondevice (100) provides for a micro-recirculation loop which allowseffective delivery of fluid for ejection.

The flow through the recirculation loop is provided in part by apressure differential between the input channel (728) and the outputchannel (730). Such a pressure differential is provided by a pressuredfluid source (838) that is fluidically coupled to the input channel(728) and output channel (730), but remote from the fluid ejectiondevice (100). Pressurized fluid source (838) creates a pressure gradientacross the ejection chamber (106) such that the fluid supplied bypressurized fluid source (838) is circulated through and across theejection chamber (106), reducing particle settling and transferringexcess heat away from the ejector. The fluid discharged away from theejection chamber (106) is not permitted to remix with the fluid enteringthe ejection chamber (106). As a result, any heat introduced by theejector (734) is transferred away from the ejection chamber (106). Inaddition, because the pressurized fluid source (838) is remote from thefluid ejection device (100), pressurized fluid source (838) does notintroduce additional heat to the fluid ejection device (100) or to theejection chamber (106). As a result, fluid ejection errors caused bynon-uniform or excessive temperature of the fluid within the ejectionchamber (106) may be reduced.

As described above, in some cases it may be desirable to alter the fluidflow rate between the inlet passage (110) and the outlet passage (112).Accordingly, a micropump (108) fluidically coupled to a nozzle (102) maybe actuated to either augment the flow in the differential flowdirection or to counter the flow in the differential flow direction asdescribed above. Thus, a customized flow past each nozzle (102) may begenerated.

FIGS. 9A and 9B are cross-sectional views of the fluid ejection device(100) with micropumps (108) and pressure-difference based fluid flow,according to an example of the principles described herein.Specifically, FIG. 9A is a cross-sectional diagram taken along the lineB-B in FIG. 6 and FIG. 9B is an example with two micropumps (108 a, 108b), each disposed proximate to one of the inlet passage (110) and theoutlet passage (112). Doing so allows for increased control as a fluidflow through an ejection chamber (106) may be increased at one point intime or decreased at another point in time. Thus, greater control isafforded to the fluid ejection system in controlling fluid flow rates.FIGS. 9A and 9B also clearly show the fluid flow from the input channel(728), through the inlet passage (110), through the ejection chamber(106) and out the outlet passage (112) to the output channel (730).FIGS. 9A and 9B also clearly depicts the rib (736) disposed underneaththe ejector (734) to provide mechanical rigidity and stability to thefluid ejection device (100). As described above and as indicated inother figures, activation of the micropump (108) may serve to augment orcounter the differential-based flow (114). Moreover, as the fluid passesby the ejector (734), the ejector (734) can be activated to expel fluidthrough the nozzle (102). The fluid ejection device (100) can be used torecirculate fluid such that fresh fluid is always provided to theejection chamber (106), which fresh fluid results in a higher qualityprinted product.

FIG. 10 is a flowchart of a method (1000) for fluid ejection withmicropumps (FIG. 1B, 108) and pressure-difference based fluid flow,according to another example of the principles described herein. Asdescribed above, fluid is circulated through an ejection chamber (FIG.1B, 106) at a pressure differential. In some examples, this may includeinputting (block 1001) fluid at the first pressure to input channels(FIG. 7, 728) that are fluidically coupled to respective ejectionchambers (FIG. 1B, 106) and to output (block 1002) the fluid at a secondpressure form output channels (FIG. 7, 730) that are fluidically coupledto respective ejection chambers (FIG. 1B, 106). This may be performed bya pressurized fluid source (FIG. 8, 838). Following such input andoutput, as described above, the circulation may be selectively adjusted(block 1003) by activating micropumps (FIG. 1B, 108).

FIG. 11 is a planar view of a fluid ejection device (100) withmicropumps (10 b) and pressure-difference based fluid flow, according toanother example of the principles described herein. For simplicity, inFIG. 11 a single instance of various components are indicated with areference number.

In the example depicted in FIG. 11, the number of ejection chambers(FIG. 1B, 106) and corresponding nozzles (102) and ejectors (734) doesnot match the number of inlet passages (110), outlet passages (112),and/or fluid micropumps (108). For example, as depicted in FIG. 11, thefluid ejection device may include six nozzles (102), ejectors (734), andcorresponding ejection chambers (FIG. 1B, 106), the fluid ejectiondevice (100) may include fewer micropumps (108 a-c). That is, in thisexample, one micropump (108) may direct flow to multiple ejectionchambers (FIG. 1B, 106). For example, a flow (114) of fluid may pass byeach nozzle (102) with a first flow rate. This flow rate is adjusted asa flow (218 a-b) resulting from an actuation of a micropump (108)combines with the differential flow (114). Such a system may simplifythe manufacture of the fluid ejection device (100) as fewer micropumps(108) may be used in the system.

Still further, the number of ejection chambers (FIG. 1B, 106), nozzles(102), and ejectors (734) may be greater or less than the number ofinlet passages (110) and outlet passage (112). For example, as depictedin FIG. 11, the fluid ejection system (100) may include six ejectionchambers (FIG. 1B, 106), nozzles (102), and ejectors (734), but mayinclude three each of an inlet passage (110 a-c), and an outlet passage(112 a-c). Doing so may provide different fluid dynamics which may bedesirable for any number of reasons. For example, if more inlet passages(110 a-c) are provided than nozzles (102), the ejection chambers (FIG.1B, 106) may refill at a faster rate and be less susceptible to failureif one inlet passage (110 a-c) becomes blocked.

Moreover, while FIG. 9 depicts a certain number, orientation, and sizeof micro-pumps (108), inlet passages (110), and outlet passages (112),any number size, and orientation of these components may be implementedin accordance with the principles described herein.

FIG. 11 also depicts the chamber walls (732) that define in part thedifferent ejection chambers (FIG. 1B, 106). In the example depicted inFIG. 11, the fluid may pool as it is received through the inlet passages(110 a-c). That is, fluid may not pass through well-defined ejectionchambers (FIG. 1B, 106). Accordingly, the chamber walls (732) serve toguide fluid flow past and the ejection chambers (FIG. 1B, 106).

FIG. 12 is a diagram of a fluid ejection device (100) with micropumps(108 a-b) and pressure-difference based fluid flow, according to anotherexample of the principles described herein. In some examples, adjacentoutlet passages (112 a-b) that correspond to adjacent ejection chambers(FIG. 1B, 106) are fluidically coupled to a common fluid output channel(730). FIG. 112 depicts such an example. In the example depicted in FIG.12, the micropumps (108 a-b) are disposed upstream of the nozzles (FIG.1A, 102) and ejectors (734 a-b). However, in other examples, the fluidmicropumps (108 a-b) may be disposed downstream of the nozzles (FIG. 1A,102) and ejectors (734 a-b).

In this example, fluid at a first pressure, P1, is passed to the fluidejection device (100) via a first input channel (728 a). As describedabove, the fluid moves through a first inlet passage (110 a) past afirst fluid micropump (108 a) and first ejector (734 a) to be expelledinto the common output channel (730) via a first outlet passage (112 a).In this example, a second pressure, P2, is generated in the outputchannel (730), which second pressure, P2, is less than the firstpressure, P1.

Similarly, fluid at a first pressure, P1, is passed to the fluidejection device (100) via a second input channel (728 b). As describedabove, the fluid moves through a second inlet passage (110 b) past asecond micropump (108 b) and second ejector (636 b) to be expelled intothe common output channel (730) via a second outlet passage (112 b). Inthis example, a second pressure, P2, is generated in the output channel(730). Such a system where adjacent ejection chambers (FIG. 1B, 106)empty into a common output channel (730) provides even morepossibilities for the configuration of a fluid ejection system (100) andcan reduce the size and cost of the fluid ejection device (100) byrelying on fewer output channels (730) and associated fluidicinterconnections and components.

FIG. 13 is a diagram of a fluid ejection device (100) with micropumps(108 a-b) and pressure-difference based fluid flow, according to anotherexample of the principles described herein. In some examples, adjacentinlet passages (110 a-b) that correspond to adjacent ejection chambers(FIG. 1B, 106) are fluidically coupled to a common fluid input channel(728). FIG. 13 depicts such an example. In the example depicted in FIG.13, the fluid micropumps (108 a-b) are disposed downstream of thenozzles (FIG. 1A, 102) and ejectors (734 a-b). However, in otherexamples, the fluid micropumps (108 a-b) may be disposed upstream of thenozzles (FIG. 1A, 102) and ejectors (734 a-b).

In this example, fluid at a first pressure, P1, is passed to the fluidejection device (100) via a common input channel (728). As describedabove, the fluid moves through a first inlet passage (110 a) past afirst fluid micropump (108 a) and first ejector (734 a) to be expelledinto the first output channel (730 a) via a first outlet passage (112a). In this example, a second pressure, P2, is generated in the firstoutput channel (730 a). Which second pressure, P2, is less than thefirst pressure, P1.

Similarly, fluid at a first pressure, P1, is passed to the fluidejection device (100) via the common input channel (728). As describedabove, the fluid moves through a second inlet passage (110 b) past asecond fluid micropump (108 b) and second ejector (734 b) to be expelledinto the second output channel (730 b) via a second outlet passage (112b). In this example, a second pressure, P2, is generated in the secondoutput channel (730 b). Such a system where adjacent ejection chambers(FIG. 1B, 106) draw from a common input channel (728) provides even morepossibilities for the configuration of a fluid ejection system (100) andcan reduce the size and cost of the system by requiring less outputchannels and associated fluidic interconnections and components

FIG. 14 is a diagram of a fluid ejection device (100) with micropumps(108) and pressure-difference based fluid flow, according to anotherexample of the principles described herein. In some examples, thenozzles (102), ejectors (734), and micropumps (108) may not align withone another along a column of nozzles (102). That is, as describedabove, the plurality of nozzles (102) disposed on a fluid ejectiondevice (100) may be arranged into particular columns. In some examples,such as that depicted in FIG. 14, the nozzles (102) and ejectors (734)may not align with one another. Moreover, in these examples, thecorresponding micropumps (108) also may be staggered in a directionperpendicular to the direction of flow through the ejection chambers(FIG. 1B, 106). Such nozzle arrangements may provide for a moreefficient drop pattern, and thereby a higher print quality.

FIGS. 15A-15C are views of fluid ejection devices (100) with micropumps(FIG. 1B, 108) and pressure-difference based fluid flow, according toanother example of the principles described herein. Specifically, FIG.15A provides an example fluid ejection device (100) that includes aplurality of nozzles (102 a-x) arranged along the device length and thedevice width in at least four nozzle columns (1540 a-d). In thisexample, a set of neighboring nozzles (102 a-x) may include four nozzles(e.g., a first set of neighboring nozzles may be a first nozzle (102 a)through a fourth nozzle (102 d)). Furthermore, nozzles within aneighboring nozzle group may be arranged along a diagonal (1542) withrespect to the length and width of the fluid ejection device (100). Anexample angle of orientation (1542) is provided between the first nozzle(102 a) and a second nozzle (102 b), where the angle of orientation(1544) may correspond to the diagonal (1542) along which neighboringnozzles may be arranged. In some examples, the diagonal (1542) alongwhich neighboring nozzles (102 a-x) may be arranged may be oblique withrespect to the length of the fluid ejection device (100), and thediagonal (1542) may be oblique with respect to the width of the fluidejection device (100). In examples, each set of neighboring nozzles(e.g., the first nozzle (102 a) to the fourth nozzle (102 d); a fifthnozzle (102 e) to an eighth nozzle (102 h); etc.) may be arranged alongparallel diagonals. Similarly the channels (728, 730) and ribs (736) maybe arranged in an oblique orientation with respect to the nozzle columns(1540).

FIG. 15B provides a cross-sectional view along view line C-C of FIG.15A, and FIG. 15C provides a cross-sectional view of the example fluidicejection device (100) of FIG. 15A along view line D-D. In this example,the fluid ejection device (100) includes an array of ribs (676 a-c) thatdefine the input channels (728 a-b) and output channels (730 a-b).Furthermore, the cross-sectional view of FIG. 15B includes dashed linedepictions of the fourth nozzle (102 d), a seventh nozzle (102 g), andan 11th nozzle (102 k) to illustrate the relative positioning of suchnozzles (102 d, 102 g, 102 k) with respect to the ribs (736 a-c) of thearray of ribs and the channels (728 a-b, 730 a-b) defined thereby.Referring to FIG. 15C, this figure includes dashed line representationsof a 21st nozzle (102 u), a 22nd nozzle (102 v), a 23rd nozzle (102 w),and a 24th nozzle (102 x).

Furthermore, it may be appreciated that the view line C-C along whichthe cross-sectional view is presented is approximately orthogonal to thediagonal (1542) along which sets of neighboring nozzles may be arranged.Accordingly, other nozzles of the neighboring nozzle sets in which thefourth nozzle (102 d), the seventh nozzle (102 g), and the 11th nozzle(102 k) are grouped may be aligned with the depicted nozzles in thecross-sectional view. Similarly, it may be appreciated that othernozzles of the first nozzle column (1540 a), second nozzle column (1540b), third nozzle column (1540 c), and fourth nozzle column (1540 d) maybe aligned with the example nozzles (102 u-x) illustrated in thecross-sectional view of FIG. 15C.

In addition, as shown in dashed line, each respective nozzle (102 d, 102g, 102 k, 102 u-x) may be fluidically coupled to a respective fluidejection chamber 106 a-c, 106 u-x. While not shown, the fluid ejectiondevice (100) may include, in each fluid ejection chamber (106 a-c, 106u-x) at least one ejector. Furthermore each fluid ejection chamber (10ca-c, 106 u-x) may include a micropump (108 a-c). Furthermore, eachrespective fluid ejection chamber (106 a-c, 106 u-x) may be fluidicallycoupled to a respective inlet passage (110 a-c), and each respectivefluid ejection chamber (106 a-c, 106 u-x) may be fluidically coupled toa respective outlet passage (112 a-c). In the cross-sectional view ofFIG. 15C, the inlet passages, and micropumps are not shown, as thecross-sectional view line is positioned such that the inlet passages andmicropumps are not included. The outlet passages (112 u-x) for arespective ejection chamber (106 u-x) are illustrated in dashed linebecause it may be spaced apart from the view line.

In this example, a top surface of each rib (736 a-c) of the array ofribs may be adjacent to and engage with a bottom surface (1546) of asubstrate (1548) in which the ejection chambers and passages may be atleast partially formed. Accordingly, the bottom surface (1546) of thesubstrate may form an interior surface of the input channels (728 a-b)and output channels (730 a-b). As shown in FIG. 15B, the bottom surface(1546) of the substrate may be opposite a top surface (1550) of thesubstrate (1548), where the top surface (1550) of the substrate (1548)may be adjacent a nozzle layer (1552) in which the nozzles (102 d, 102g, 102 k) may be formed. In this example, a portion of the fluidejection chambers (106 a-c, 106 u-x) may be defined by a surface of thenozzle layer (1552) disposed above the portion of the fluid ejectionchambers (106 a-c) formed in the substrate (1548). In other examples,ejection chambers, nozzles, and feed holes may be formed in more or lesslayers and substrates. A bottom surface of each rib (736 a-c) may beadjacent to a top surface (1554) of an interposer (1556). Accordingly,in this example, the input channels (728 a-b) and output channels (730a-b) may be defined by the ribs (736 a-c), the substrate (1548), and theinterposer (1556). Accordingly, as shown FIGS. 15B-15C, the fluidejection device (100) includes an array of passages (110 a-c, 112 a-c,112 u-x) formed through the bottom surface of the fluid ejection device(100).

In examples similar to the example of FIGS. 15A-C, channels may bearranged to facilitate circulation of fluid through ejection chambers.In the example, the inlet passages (110 a-c) may be fluidically coupledto a respective input channel (728 a-b) such that fluid may be conveyedfrom the respective input channel (728 a-b) to the respective fluidejection chamber (106 a-c, 106 u-x) via the respective inlet passage(110 a-c). Similarly, each respective outlet passage (112 a-c, 112 u-x)may be fluidically coupled to a respective output channel (730 a-b) suchthat fluid may be conveyed from the respective fluid ejection chamber(106 a-c, 106 u-x to the respective output channel (730 a-b) via therespective outlet passages (112 a-c, 112 u-x). The respective inputchannels (728 a-b) and the respective output channels (730 a-b) may befluidly separated by the ribs (736 a-c) along some portions of thedevice such that fluid flow may occur solely through the passages (110a-c, 112 a-c) and the ejection chambers (106 a-c).

Some fluid input to the ejection chambers (106 a-c) may be ejected viathe nozzles (102 d, 102 g, 102 k) as fluid drops. However, to facilitatecirculation through the ejection chambers (106 a-c), some fluid may beconveyed from the ejection chambers (106 a-c) back to the respectiveoutput channels (730 a-b).

Referring to FIGS. 15A and 15B, it should be noted that the ribs (735a-c) of the array of ribs, and the channels (728 a-b, 730 a-b) partiallydefined thereby may be parallel to the diagonals (1542) through whichneighboring nozzles (102 a-x) are also arranged. Furthermore, as shown,in this example, the respective inlet passages of nozzles (102 a-x) ofsets of neighboring nozzles may be commonly coupled to a respectiveinput channel (728 a-b), and the respective outlet passages of nozzles(102 a-x) of sets of neighboring nozzles may be commonly coupled to arespective output channel (730 a-b). In this example, the fluidicarrangement of the ejection chambers (106 a-c), the inlet passages (110a-c), and the outlet passages (112 a-c) may be described as straddlingrespective ribs (736 a-c) of the array of ribs.

For example, as shown in FIG. 15B, the respective inlet passage (110 b)coupled to the seventh nozzle (102 g) and the respective inlet passage(110 c) coupled to the 11th nozzle (102 k) are fluidically coupled to arespective input channel (728). Similarly, the respective outlet passage(112 a) coupled to the fourth nozzle (102 d) and the respective outletpassage (112 b) coupled to the seventh nozzle (102 g) are fluidicallycoupled to a respective output channel (730 a-b). Since neighboringnozzles (102 a-x) are aligned with the nozzles (102 d, 102 g, 102 k)shown in FIG. 15B along a respective rib (736 a-c), it may be noted thatpassages associated with neighboring nozzles of each respective nozzleshown (102 d, 102 g, 102 k) may be similarly arranged.

As shown in FIG. 15B, ejection chambers (106 a-c) may be disposed in thesubstrate above respective ribs (736 a-c), and the passages (110 a-c,112 a-c) coupled to a respective ejection chamber (106 a-c) may bepositioned on opposite sides of the respective rib (736 a-c) such thatfluid input to the respective ejection chamber (106 a-c) via therespective inlet passage (110 a-c) may be fluidly separated from fluidoutput from the respective ejection chamber (106 a-c) via the respectiveoutlet passage (112 a-c).

As shown in FIGS. 15B-C, the top surface (1554) of the interposer (1556)may form a surface of the channels (728 a-b, 730 a-b). Furthermore, theinterposer (1556) may be positioned with respect to the substrate (1548)and the ribs (736 a-c) such that a fluid input (1558) and a fluid output(1560) may be at least partially defined by the interposer (1556) and/orthe substrate (1548). In such examples, the fluid input (1558) may befluidically coupled to the channels (728 a-b, 730 a-b), and the fluidoutput (1560) may be fluidically coupled to the channels (728 a-b, 730a-b).

FIG. 16 is a block diagram of a fluid ejection device (100) withmicropumps (108) and pressure-difference based fluid circulation,according to another example of the principles described herein. FIG. 16depicts the fluid ejection device (100) which includes a plurality ofnozzles (102-1, 102-n) distributed across a length and width of thefluid ejection device (100) such that at least one respective pair ofneighboring nozzles are positioned at different width positions alongthe width of the fluid ejection device (100). The fluid ejection device(100) further includes a plurality of ejection chambers (106-1, 106-n)that includes, for each respective nozzle (102), a respective ejectionchamber (106) that is fluidically coupled to the nozzle (102). The fluidejection device (100) further includes at least one fluid actuatordisposed in each ejection chamber (106). The fluid ejection device (100)further includes an array of inlet passages (110-1, 110-n) and outletpassages (112-1, 112-n) formed on a surface of the fluid ejection device(100) opposite a surface through which the nozzles (102) are formed. Inthis example, the array of inlet passages (110) and outlet passages(112) includes at least one respective passage (110, 112) fluidicallycoupled to each ejection chamber (106). FIG. 16 also depicts themicropump (108) coupled to ejection chambers (106) to adjust a flow ratethrough the ejection chambers (106).

FIG. 17 is a block diagram of a fluid ejection system (1758) withpressure-difference based fluid circulation, according to anotherexample of the principles described herein. In this example, the fluidejection device (100) includes the nozzles (102) and ejection chambers(106) as described above. The fluid ejection device (100) also includesmicropump(s) (108). In some examples, the micropump(s) may be coupled toone or many ejection chambers (106).

In this example, each respective inlet passage (110) may be fluidicallycoupled to a respective input channel (728), and each respective outletpassage (112) may be fluidically coupled to a respective output channel(730).

The fluid ejection system (1758) also includes a fluid supply system(1760) that supplied fluid to the fluid ejection device (100). A fluidsupply system may include fluid supply components, such as pumps (1762a-b) to drive fluid towards the fluid ejection device (100). The fluidsupply system (1760) may also include other components such asregulators, tanks, and other such components that apply fluid pressuredifferentials to the fluid supply system and fluid ejection devicesconnected thereto to thereby drive fluid through these fluid supplycomponents and fluid ejection devices connected thereto. To furthergenerate the pressure differential, the fluid ejection device (100)includes an input regulator (1764 a) fluidically coupled to the fluidsupply system (1730) and the input channel (728). The input regulator(1764 a) establishes a first pressure for supply fluid. The fluidejection device (100) also includes an output regulator (1764 b)fluidically coupled to the fluid supply system (1730) and the outputchannel (728). The output regulator (1764 g) establishes a secondpressure for collected fluid.

What is claimed is:
 1. A fluid ejection device, comprising: a pluralityof nozzles; a plurality of ejection chambers, comprising a respectiveejection chamber of the plurality of ejection chambers fluidicallycoupled to a respective nozzle of the plurality of nozzles; a pluralityof inlet passages which are fluidically coupled to the ejection chambersand input fluid to the ejection chambers at a first pressure; aplurality of outlet passages which are fluidically coupled to theejection chambers and to output fluid from the ejection chambers at asecond pressure that is less than the first pressure such that fluidcirculates through the ejection chambers based on the pressuredifference between the first pressure and the second pressure; and atleast one micropump fluidically coupled to ejection chambers to pumpfluid through the ejection chambers.
 2. The fluid ejection device ofclaim 1, wherein the at least one micropump is disposed proximate to therespective ejection chamber.
 3. The fluid ejection device of claim 2,wherein the at least one micropump is upstream of a nozzle fluidicallycoupled to a respective ejection chamber to increase a flow rate throughthe respective ejection chamber.
 4. The fluid ejection device of claim2, wherein the at least one micropump is downstream of a nozzlefluidically coupled to a respective ejection chamber to decrease a flowrate through the respective ejection chamber.
 5. The fluid ejectiondevice of claim 1, wherein the at least one micropump comprises athermal resistor.
 6. The fluid ejection device of claim 1, wherein: theat least one micropump comprises a piezoelectric membrane; anddeflection of the piezoelectric membrane changes a flow rate through theat least one ejection chamber.
 7. A fluid ejection device comprising: aplurality of nozzles; a plurality of ejection chambers, comprising arespective ejection chamber of the plurality of ejection chambersfluidically coupled to a respective nozzle of the plurality of nozzles;a plurality of inlet passages, comprising a respective inlet passagefluidically coupled to the respective ejection chamber; a plurality ofoutlet passages, comprising a respective outlet passage fluidicallycoupled to the respective ejection chamber; at least one input channel,the at least one input channel fluidically coupled to at least a subsetof inlet passages of the plurality of inlet passages, the at least oneinput channel to supply fluid to the subset of inlet passages at a firstpressure; at least one output channel, the at least one output channelfluidically coupled to at least a subset of outlet passages of theplurality of outlet passages, the at least one output channel to receivefluid from the subset of outlet passages at a second pressure differentthan the first pressure to thereby facilitate fluid circulation throughejection chambers fluidically coupled to the subset of inlet passagesand the subset of outlet passages; and at least one micropumpfluidically coupled to at least one ejection chamber to pump fluidthrough the at least one ejection chamber.
 8. The fluid ejection deviceof claim 7, wherein a number of ejection chambers is greater than atleast one of: a number of inlet passages; and a number of outletpassages.
 9. The fluid ejection device of claim 7, wherein a number ofejection chambers is greater than a number of micropumps.
 10. The fluidejection device of claim 7, wherein adjacent outlet passagescorresponding to adjacent ejection chambers are fluidically coupled to acommon output channel.
 11. The fluid ejection device of claim 7, whereinadjacent inlet passages corresponding to adjacent ejection chambers arefluidically coupled to a common input channel.
 12. The fluid ejectiondevice of claim 7, further comprising an array of ribs that define theat least one input channel and the at least one output channel, wherein:the plurality of nozzles are arranged in nozzle columns; the pluralityof nozzles are arranged in respective sets of neighboring nozzles thatare diagonally arranged with respect to the length and the width of thefluid ejection device; the ribs of the array of ribs, the at least oneinput channel, and the at least one output channel are aligned with thediagonal arrangements of the respective sets of neighboring nozzles. 13.The fluid ejection device of claim 7, further comprising: an inputregulator to generate the first pressure in the fluid at the at leastone input channel; and an output regulator to generate the secondpressure in the fluid at the at least one output channel.
 14. A method,comprising: circulating fluid through a plurality of ejection chambersat a first flow rate by: supplying fluid to the plurality of ejectionchambers at a first pressure; and collecting fluid from the plurality ofejection chambers at a second pressure that is lower than the firstpressure; and selectively adjusting circulation of fluid through atleast one ejection chamber to a second flow rate by actuating at leastone micropump fluidically coupled to the at least one ejection chamber.15. The method of claim 14, wherein circulating fluid through theplurality of ejection chambers at the first flow rate by supplying fluidto the plurality of ejection chambers at the first pressure andcollecting fluid from the plurality of ejection chambers at the secondpressure comprises: inputting fluid at the first pressure to a pluralityof input channels that are each fluidically coupled to a respectiveejection chamber of the plurality of ejection chambers; and outputtingfluid at the second pressure from a plurality of output channels thatare each fluidically coupled to one of the respective ejection chambers.